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Diffstat (limited to 'lib/reed_solomon/reed_solomon.c')
| -rw-r--r-- | lib/reed_solomon/reed_solomon.c | 335 |
1 files changed, 335 insertions, 0 deletions
diff --git a/lib/reed_solomon/reed_solomon.c b/lib/reed_solomon/reed_solomon.c new file mode 100644 index 0000000..6604e3b --- /dev/null +++ b/lib/reed_solomon/reed_solomon.c @@ -0,0 +1,335 @@ +/* + * lib/reed_solomon/rslib.c + * + * Overview: + * Generic Reed Solomon encoder / decoder library + * + * Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de) + * + * Reed Solomon code lifted from reed solomon library written by Phil Karn + * Copyright 2002 Phil Karn, KA9Q + * + * $Id: rslib.c,v 1.5 2004/10/22 15:41:47 gleixner Exp $ + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * Description: + * + * The generic Reed Solomon library provides runtime configurable + * encoding / decoding of RS codes. + * Each user must call init_rs to get a pointer to a rs_control + * structure for the given rs parameters. This structure is either + * generated or a already available matching control structure is used. + * If a structure is generated then the polynomial arrays for + * fast encoding / decoding are built. This can take some time so + * make sure not to call this function from a time critical path. + * Usually a module / driver should initialize the necessary + * rs_control structure on module / driver init and release it + * on exit. + * The encoding puts the calculated syndrome into a given syndrome + * buffer. + * The decoding is a two step process. The first step calculates + * the syndrome over the received (data + syndrome) and calls the + * second stage, which does the decoding / error correction itself. + * Many hw encoders provide a syndrome calculation over the received + * data + syndrome and can call the second stage directly. + * + */ + +#include <linux/errno.h> +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/module.h> +#include <linux/rslib.h> +#include <linux/slab.h> +#include <asm/semaphore.h> + +/* This list holds all currently allocated rs control structures */ +static LIST_HEAD (rslist); +/* Protection for the list */ +static DECLARE_MUTEX(rslistlock); + +/** + * rs_init - Initialize a Reed-Solomon codec + * + * @symsize: symbol size, bits (1-8) + * @gfpoly: Field generator polynomial coefficients + * @fcr: first root of RS code generator polynomial, index form + * @prim: primitive element to generate polynomial roots + * @nroots: RS code generator polynomial degree (number of roots) + * + * Allocate a control structure and the polynom arrays for faster + * en/decoding. Fill the arrays according to the given parameters + */ +static struct rs_control *rs_init(int symsize, int gfpoly, int fcr, + int prim, int nroots) +{ + struct rs_control *rs; + int i, j, sr, root, iprim; + + /* Allocate the control structure */ + rs = kmalloc(sizeof (struct rs_control), GFP_KERNEL); + if (rs == NULL) + return NULL; + + INIT_LIST_HEAD(&rs->list); + + rs->mm = symsize; + rs->nn = (1 << symsize) - 1; + rs->fcr = fcr; + rs->prim = prim; + rs->nroots = nroots; + rs->gfpoly = gfpoly; + + /* Allocate the arrays */ + rs->alpha_to = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL); + if (rs->alpha_to == NULL) + goto errrs; + + rs->index_of = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL); + if (rs->index_of == NULL) + goto erralp; + + rs->genpoly = kmalloc(sizeof(uint16_t) * (rs->nroots + 1), GFP_KERNEL); + if(rs->genpoly == NULL) + goto erridx; + + /* Generate Galois field lookup tables */ + rs->index_of[0] = rs->nn; /* log(zero) = -inf */ + rs->alpha_to[rs->nn] = 0; /* alpha**-inf = 0 */ + sr = 1; + for (i = 0; i < rs->nn; i++) { + rs->index_of[sr] = i; + rs->alpha_to[i] = sr; + sr <<= 1; + if (sr & (1 << symsize)) + sr ^= gfpoly; + sr &= rs->nn; + } + /* If it's not primitive, exit */ + if(sr != 1) + goto errpol; + + /* Find prim-th root of 1, used in decoding */ + for(iprim = 1; (iprim % prim) != 0; iprim += rs->nn); + /* prim-th root of 1, index form */ + rs->iprim = iprim / prim; + + /* Form RS code generator polynomial from its roots */ + rs->genpoly[0] = 1; + for (i = 0, root = fcr * prim; i < nroots; i++, root += prim) { + rs->genpoly[i + 1] = 1; + /* Multiply rs->genpoly[] by @**(root + x) */ + for (j = i; j > 0; j--) { + if (rs->genpoly[j] != 0) { + rs->genpoly[j] = rs->genpoly[j -1] ^ + rs->alpha_to[rs_modnn(rs, + rs->index_of[rs->genpoly[j]] + root)]; + } else + rs->genpoly[j] = rs->genpoly[j - 1]; + } + /* rs->genpoly[0] can never be zero */ + rs->genpoly[0] = + rs->alpha_to[rs_modnn(rs, + rs->index_of[rs->genpoly[0]] + root)]; + } + /* convert rs->genpoly[] to index form for quicker encoding */ + for (i = 0; i <= nroots; i++) + rs->genpoly[i] = rs->index_of[rs->genpoly[i]]; + return rs; + + /* Error exit */ +errpol: + kfree(rs->genpoly); +erridx: + kfree(rs->index_of); +erralp: + kfree(rs->alpha_to); +errrs: + kfree(rs); + return NULL; +} + + +/** + * free_rs - Free the rs control structure, if its not longer used + * + * @rs: the control structure which is not longer used by the + * caller + */ +void free_rs(struct rs_control *rs) +{ + down(&rslistlock); + rs->users--; + if(!rs->users) { + list_del(&rs->list); + kfree(rs->alpha_to); + kfree(rs->index_of); + kfree(rs->genpoly); + kfree(rs); + } + up(&rslistlock); +} + +/** + * init_rs - Find a matching or allocate a new rs control structure + * + * @symsize: the symbol size (number of bits) + * @gfpoly: the extended Galois field generator polynomial coefficients, + * with the 0th coefficient in the low order bit. The polynomial + * must be primitive; + * @fcr: the first consecutive root of the rs code generator polynomial + * in index form + * @prim: primitive element to generate polynomial roots + * @nroots: RS code generator polynomial degree (number of roots) + */ +struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim, + int nroots) +{ + struct list_head *tmp; + struct rs_control *rs; + + /* Sanity checks */ + if (symsize < 1) + return NULL; + if (fcr < 0 || fcr >= (1<<symsize)) + return NULL; + if (prim <= 0 || prim >= (1<<symsize)) + return NULL; + if (nroots < 0 || nroots >= (1<<symsize) || nroots > 8) + return NULL; + + down(&rslistlock); + + /* Walk through the list and look for a matching entry */ + list_for_each(tmp, &rslist) { + rs = list_entry(tmp, struct rs_control, list); + if (symsize != rs->mm) + continue; + if (gfpoly != rs->gfpoly) + continue; + if (fcr != rs->fcr) + continue; + if (prim != rs->prim) + continue; + if (nroots != rs->nroots) + continue; + /* We have a matching one already */ + rs->users++; + goto out; + } + + /* Create a new one */ + rs = rs_init(symsize, gfpoly, fcr, prim, nroots); + if (rs) { + rs->users = 1; + list_add(&rs->list, &rslist); + } +out: + up(&rslistlock); + return rs; +} + +#ifdef CONFIG_REED_SOLOMON_ENC8 +/** + * encode_rs8 - Calculate the parity for data values (8bit data width) + * + * @rs: the rs control structure + * @data: data field of a given type + * @len: data length + * @par: parity data, must be initialized by caller (usually all 0) + * @invmsk: invert data mask (will be xored on data) + * + * The parity uses a uint16_t data type to enable + * symbol size > 8. The calling code must take care of encoding of the + * syndrome result for storage itself. + */ +int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par, + uint16_t invmsk) +{ +#include "encode_rs.c" +} +EXPORT_SYMBOL_GPL(encode_rs8); +#endif + +#ifdef CONFIG_REED_SOLOMON_DEC8 +/** + * decode_rs8 - Decode codeword (8bit data width) + * + * @rs: the rs control structure + * @data: data field of a given type + * @par: received parity data field + * @len: data length + * @s: syndrome data field (if NULL, syndrome is calculated) + * @no_eras: number of erasures + * @eras_pos: position of erasures, can be NULL + * @invmsk: invert data mask (will be xored on data, not on parity!) + * @corr: buffer to store correction bitmask on eras_pos + * + * The syndrome and parity uses a uint16_t data type to enable + * symbol size > 8. The calling code must take care of decoding of the + * syndrome result and the received parity before calling this code. + */ +int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len, + uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk, + uint16_t *corr) +{ +#include "decode_rs.c" +} +EXPORT_SYMBOL_GPL(decode_rs8); +#endif + +#ifdef CONFIG_REED_SOLOMON_ENC16 +/** + * encode_rs16 - Calculate the parity for data values (16bit data width) + * + * @rs: the rs control structure + * @data: data field of a given type + * @len: data length + * @par: parity data, must be initialized by caller (usually all 0) + * @invmsk: invert data mask (will be xored on data, not on parity!) + * + * Each field in the data array contains up to symbol size bits of valid data. + */ +int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par, + uint16_t invmsk) +{ +#include "encode_rs.c" +} +EXPORT_SYMBOL_GPL(encode_rs16); +#endif + +#ifdef CONFIG_REED_SOLOMON_DEC16 +/** + * decode_rs16 - Decode codeword (16bit data width) + * + * @rs: the rs control structure + * @data: data field of a given type + * @par: received parity data field + * @len: data length + * @s: syndrome data field (if NULL, syndrome is calculated) + * @no_eras: number of erasures + * @eras_pos: position of erasures, can be NULL + * @invmsk: invert data mask (will be xored on data, not on parity!) + * @corr: buffer to store correction bitmask on eras_pos + * + * Each field in the data array contains up to symbol size bits of valid data. + */ +int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len, + uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk, + uint16_t *corr) +{ +#include "decode_rs.c" +} +EXPORT_SYMBOL_GPL(decode_rs16); +#endif + +EXPORT_SYMBOL_GPL(init_rs); +EXPORT_SYMBOL_GPL(free_rs); + +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("Reed Solomon encoder/decoder"); +MODULE_AUTHOR("Phil Karn, Thomas Gleixner"); + |
